Submarine signal microphone



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Iv H In I. n I In Aug. 12, 1947. w. J. BROWN S UBNARINE SIGNAL MICROPHONE Filed March 4,- 1943 Patented Aug. 12, 1947 SUBMARINE SIGNAL MICROPHONE William J. Brown, West En glewood, N. .l., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application March 4, 1943, Serial No. 477,922

I Y 4 Claims.

This invention relates to submarine signaling devices and more particularly to microphones of the type adapted to be mounted on or in the hull of a ship and responsive to submarine signals.

Microphones mounted on or in the hull of a ship are subjected to actuating forces due to two sources, namely, the signal sounds transmitted thereto through the sea and the noises within the ship itself. The noises, of course, result in interference with and distortion of the signals translated by the microphones and the magnitude of the effect thereof may become sufiicient to render the output of the microphone unintelligible, having poor correspondence to the signal intended to be translated by the microphone' One object of this invention is to improve the fidelity of translation of signals by a submarine signaling device. More specifically one object of this invention is to obtain a high signal to noise ratio for a microphone adapted for use in sub-' marine signaling, whereby signals'received by the microphone are translated with substantial fidelity. V

In accordance with one feature of this invention, a microphone adapted for mounting on or in the hull of a ship is constructed of two electromechanical units both of which are responsive to noises originating'on the ship and only one of which is' responsive to the submarine signals the microphone is intended to translate and the outputs of the two units are combined in such relation that the responses of the two units to noises substantially cancel each other.

The invention and the above noted and other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawing in which:

Fig. 1 is a side view partly in section illustrating one manner in which a microphone construct- 40 ed in accordance with this invention may be mounted on the hull of a ship;

Fig. 2 is a side view in section of a microphone illustrative of one embodiment of this invention;

Fig, 3 is an enlarged perspective view of one of the electromechanical translating units included in the microphone shown in Fig. 2; and

Figs. 4 and 5 are circuit diagrams illustrating ways in which the microphone shown in Fig. 2 may be operated.

Referring now to the drawing, the microphone illustrated in Fig. 2 comprises a base or foundation plate Ill of substantial mass, for example of metal, and two circular caps II, also for example of metal, secured to the base of foundation plate 5 form of vibrations,

.is shown at I3 in Fig. 1, one of the caps I I fitting surface in direct contact with the sea.

Each of the caps II is provided with a central, circular diaphragm portion l4 connected to the body of the cap by a relatively thin annulus I5 so that thediaphragm portions may move substantially bodily normal to their faces. Each cap is provided also with an annular groove I6 and the base or foundation member II] is provided with similar grooves each opposite one of the grooves .I 5. Seated in the juxtaposed grooves are resilient rings I l, for example of soft rubber, which are compressed by screws I8 bearing against metallic annuli I9 to form a water-tight seal between each cap I I and the base of foundation plate l0.

The microphone comprises further a pair of substantially identical electromechanical transin an aperture in the hull and having its outer lating units 20, each of which is held between the base or foundation plate I0 and one of the diaphragms I4. Each of the translating units 20, as shown more clearly in Fig, 3, includes a plurality of piezoelectric crystals 2I, for example Rochelle salt slabs or blocks, having electrodes 22, for example conductive coatings, on the ma jor faces thereof, to which suitable leading-in conductors 23 are connected. The several crystals 2| of each unit are secured together in faceto-face relation, have their similar electrical and mechanical axisparallel and are connected electrically in parallel. Each crystal assembly has secured to opposite ends thereof a thin insulating, for example ceramic, plate 24, the inner plate 24 being cemented to the base or foundation plate I0 and each of the outer plates 24 bearing against the corresponding diaphragm Id.

In the assembly'of the microphone, the screws I2 which secure the caps I I to the base or foundation plate I0 are tightened so that the two units 20 are placed under equal compression.

As illustrated in Fig. 4, in one manner of operation of the microphone, the two translating units 20 are connected to similar preamplifiers 25 and the outputs of these preamplifiers are connected in opposition to amplifier 26, the output of which is supplied to an indicating instruunent 21, such, for example, as a telephone receiver.

Noises originating on or within the ship or at the propeller thereof are transmitted, in the through the hull I3 to the base or foundation plate I and thence to both i of the translating units 20. The noise energy is translated by the units into two electrical variations or signals which are substantially of equal magnitude and opposite phase. Hence, these variations as impressed upon the input of the amplifier substantially cancel one another.

' posed of two signals, due to noise, which substantially cancel each other and a third signal corresponding to that picked up by the microphone. Thus, as will be apparent, a high signal to noise ratio is obtained and the output of the amplifier 26 corresponds to the signal picked up .by the microphone and is substantially free of distortion due to noise.

Because of dissimllarities in the two units 20, in the initial compression thereof, in the transmission of energy to the two units 20 by the plate l0 and other factors, the outputs of the two units in response to noise may not be of exactly equal magnitudes and may not be exactly 180 degrees out of phase. Departure from amplitude equality of these two outputs may be corrected by adjusting one or both of the preampliflers 25 or otherwise controlling the output of one or both units. Departures from phase opposition may be compensated for, as shown in Fig. 5, by providing an adjustable phase shifting device 28 in association with one of the units 20. This device may be connected, advantageously, between the amplifier 29 associated with the one unit and the input of a transformer 30 connected to the indicating device.

In compensating for amplitude inequality and departure from phase opposition, the preamplifiers and phase shiftin device may be adjusted under normal noise conditions and in. the absence of a submarine signal so that .the indication obtained at the indicating device is a minimum.

In a properly constructed microphone of the design shown in Fig. 2, noise cancellations of the order of 15 decibels over octave bands within the frequency range of approximately 500 to 5000 cycles per second and cancellations of single frequencies at the center of the bands of the order of 25 decibels have been obtained without either phase or amplitude compensation.

Although specific embodiments of thisinvention have been shown and described, it will be understood that they are but illustrative and that various modifications may be made therein without departing from the scope and spirit of this invention as defined in the appended claims.

What is claimed is:

1. A submarine signaling device comprising a foundation plate adapted to be mounted on the hull of a ship and responsive to vibrations transmitted therein, a pair of similar piezoelectric crystal translating units secured to opposite faces of said plate and responsive to vibrations transmitted to said plate by said hull, and diaphragm means for driving only one of said crystals in response to submarine signals.

2. A submarine signaling device comprising a plate adapted for mounting in vibration transmitting relation with the hull of a ship, a pair of caps secured to opposite faces of said plate and havingv central diaphragm portions, only one of said diaphragm portions being exposed to submarine signals, and a pair of similar translating units each secured between said plate and one of said diaphragm portions.

3. A submarine signaling device adapted to be mounted on the hull of a ship comprising a foun dation plate responsive to vibrations transmitted through said hull, a pair of aligned caps secured to opposite faces 01' said plate, .each cap having .a vibratile portion, and a pair of similar piezoelectric crystals within said caps secured to 0pposite faces of saidplate and each engaging a corresponding one of said vibratile portions, only one of said vibratile portions being exposed to submarine signals,

I 4. A submarine signaling device for mounting on the hull of a ship and adjacent an opening therein, comprising a foundation member adapted to be mounted upon the hull and extend over said opening and in vibration transmitting relation with the hull, a first electromechanical signal translating unit mounted upon the outer face of said member and responsive to vibrations thereof, means adapted to be exposed to the sea through said opening for actuating said first unit in accordance with submarine signals, and a second electromechanical signal translating unit mounted upon the inner face of said member, responsive to vibrations thereof and shielded from submarine signals.

WILLIAM J. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number .Name Date 1,312,809 Scribner et al Aug. 12, 1919 1,415,539 Fessenden May 9, 1922 2,138,036 Kunze Nov. 29, 1938 2,376,730 Steinhoff May 22, 1945 2,368,953 Walsh Feb. 6, 1945 FOREIGN PATENTS Number Country Date 567,999 Germany Jan. 12, 1933 367,935

Germany Jan. 29,1923 

